Deflagration to detonation transitions (DDTs): Predicting DDTs in hydrocarbon explosions

Abstract

This paper discusses our efforts to expand CFD calculations to include the prediction of deflagration to detonation transitions (DDTs) for various fuels including hydrogen, ethylene, propane and natural gas. The work includes validation against experiments conducted in a variety of configurations including: (1) closed pipes with obstacles; (2) other congested lab-scale geometries; (3) medium to large-scale 3-D obstacle configurations; and (4) large-scale geometries where DDT occurred upon flame propagation from confined to more open configurations. Validation of CFD models against experimental data is a critical step in verifying their accuracy in predicting DDT phenomena. In addition, an extensive set of experiments, which were performed under a variety of conditions that influence the transition to detonation, should be utilized in the validation to demonstrate the robustness of a CFD model and ensure its use for actual large-scale scenarios, i.e., petrochemical facilities where the likelihood of DDTs need to be evaluated for siting studies.The CFD model FLACS has been recently extended to identify whether DDT is likely in a given scenario and indicate the regions where it might occur. The likelihood of DDT has been expressed in terms of spatial pressure gradients across the flame front. This parameter is able to visualize when the flame front captures the pressure front, which is one of the main mechanisms that may initiate a DDT. Reasonable agreement was obtained with experimental observations in terms of explosion pressures, transition times, and flame speeds. The DDT model is currently being extended to include a criterion for estimating the likelihood of DDT by comparison of the geometric dimensions with the detonation cell size of the fuel-air mixture. This paper will provide a summary of some of the results.